Emulsion manufacturers are deeply interested in the covering power of silver halide emulsions because the use of an emulsion having a higher covering power leads to a saving of the amount of silver necessary to maintain a certain optical density.
U.S. Pat. Nos. 4,411,986, 4,434,226, 4,413,053, 4,414,304, 4,414,306, and 4,435,501 disclose that the covering power of developed silver is considerably increased by using tabular grains having a high aspect ratio and a reduced thickness.
Extremely thin tabular grains having a thickness of less than 0.07 .mu.m are disclosed in JP-A 99751/1987, 115435/1987, 43605/1994, and 43606/1994.
EP 0699944A, 0699946A, 0699947A, JP-A 101476/1997, 101475/1997, 101473/1997, 101472/1997, 69069/1997, and U.S. Pat. No. 5,494,789 disclose techniques relating to high aspect ratio tabular grains having epitaxial sites.
However, the tone of developed silver resulting from emulsion grains providing a high covering power, which depends on the size and thickness of grains, is almost always yellowish and gives an unpleasant impression to the image viewer. The tone becomes yellowish because as the size and thickness of grains decrease, the developed silver is also decreased in size and thickness so that the scattering of blue light components increases to produce more yellowish light. This phenomenon becomes a problem particularly when fine grain emulsions (e.g., mean particle size less than 0.4 .mu.m) or tabular grains having a reduced thickness (e.g., particle thickness less than 0.4 .mu.m) are used as the silver halide emulsion. In general, compounds known as toners are often used for adjusting the tone of developed silver. For example, certain mercapto compounds are used as the toner. However, even when such conventional well-known toners are applied to emulsions containing high sensitivity silver halide grains, they incur substantial desensitization and are thus impractical.
Then, as described in JP-A 154251/1985, 276539/1987, 285445/1986, and 204085/1993, it is widely practiced to control the tone by containing substantially water-insoluble dyestuffs in photosensitive elements so that the tone of developed silver may become neutral black. Also, JP-A 234035/1992, 199394/1995 and EP 655645A1 disclose that pigments are contained in photosensitive elements for adjusting the tone of developed silver and improving the residual color of a spectral sensitizing dye after processing. In this case, however, not only the transmission tone of developed silver becomes yellowish, but the reflection tone of developed silver also becomes reddish brown, giving a disgustful impression.
In general, where external light is present on observation of transmitted light, a certain proportion of reflected light is often contained therein. Thus it is desired that the reflection tone of developed silver be black. In this regard, the above-discussed prior art techniques are not satisfactory.
Moreover, these techniques have the problem that if a cleaner is left on a fluorescent intensifying screen used on radiographic photographing, the screen can be colored or stained with the dyestuff or pigment contained in the photosensitive element. Another problem is that if pressure or friction is applied to the photosensitive element during handling thereof, the dyestuff or pigment contained in the photosensitive element causes staining of the photosensitive element itself or the rubbing object.